I went hunting for the fourth treasure hoard hidden in the Toxic Valley — you have to be a special kind of crazy to go tramping through that blighted landscape voluntarily. Hopefully your Raider reputation is shining, because this route runs you straight past a crashed space station crawling with rads and a pack of amoral goons led by a cap-obsessed nihilist named Meg. Nothing cramps a free-spirited "live and let live, or kill or be killed, pick your poison" style quite like that. Anyway — where was I? Right, the treasure.
Fast-travel to The Crater — it's a free travel point, so don't let anyone charge you caps for the privilege. From the drop point, turn around and head southwest until you spot the lookout platform. Ignore the idiots on patrol; they're about as likely to shoot each other as they are to shoot you. Walk up to the platform until you're standing on the side with the stairs, then put the platform at your back and start climbing uphill. It's a rough scramble without a jetpack and a marsupial mutation, but keep at it. When you crest the second plateau, look right for a large, white dead tree — the treasure mound is sitting on the flat ground beside it.
Once you've loaded up, head into the Crater interior and hawk your loot to a vendor named Raf. Just watch yourself — he'll try to rob you blind if you let him.